This invention relates to a magnetic recording and reproducing apparatus which can read and write information in different recording periods from and on floppy disks of a magnetic media for which recording periods are different such as for 1 megabyte and 2 megabytes, and more particularly to an apparatus of the type which is improved in compatibility in writing performance with a magnetic recording and reproducing apparatus for a small storage capacity.
A floppy disk drive unit as a general magnetic recording and reproducing apparatus has come in wide use as a means for recording and reproducing information for use with a personal computer, a word processor, and so on. As general information is diversified and increased in density, it is required to be reduced in size and have an increased capacity for recording information.
Such a requirement is partially met as the technical development of magnetic recording and reproducing apparatus has progressed of late: for example, a magnetic disk of a size of 3.5 inches can store information of 2 megabytes.
However, the recording period of a floppy disk drive unit for recording and reproducing information of such a large capacity as 2 megabytes is about one half to that of a floppy disk drive unit for such a small capacity as 1 megabyte, and magnetic heads for such recording periods are different in recording and reproducing characteristics. Accordingly, information recorded in a longer recording period on a magnetic disk cannot be reproduced nor re-recorded on a floppy disk drive unit for a shorter recording period, and hence it must be rewritten once in a format of the shorter recording period, resulting in inconvenience.
Accordingly, a floppy disk drive unit is required to allow reading and writing with a single system of a magnetic disk which is recorded in a different recording period.
Now, a conventional floppy disk drive unit will be described with reference to FIG. 3 which illustrates a construction of a circuit for reading and writing information for 2 megabytes.
Referring to FIG. 3, the circuit includes a magnetic head 1, a change-over circuit 2, a preamplifier 3, a reading circuit 5, a writing circuit 8 and a filter circuit 9.
The magnetic head 1 writes and reads magnetic record data on and from a magnetic disk. The change-over circuit 2 operates in response to a changing over instruction from a host computer not shown to change over to couple signals read by the magnetic head 1 to the preamplifier 3 or alternatively to couple signals from the writing circuit 8 to the magnetic head 1.
Signals inputted from the magnetic head 1 to the preamplifier 3 via the change-over circuit 2 are amplified to a desired voltage and outputted to the filter circuit 9.
The filter circuit 9 receives signals from the preamplifier 3 over two signal lines. To one signal line, a capacitor C1, a resistor R1 and an inductor L1 are connected in series while a capacitor C2, a resistor R2 and an inductor L2 are connected in series to the other signal line.
A capacitor 7 is connected in parallel with the two signal lines between junctions between the resistor R1 and the inductor L1 and between the resistor R2 and the inductor L2. A capacitor C6 and a resistor R9 are connected in parallel relationship between one terminal end of each of the inductors L1 and L2, that is, at junctions between the filter circuit 9 and the reading circuit 5.
Thus, DC voltage components and very low frequency components of signals from the preamplifier 3 are cut by the capacitors C1 and C2 while high frequency components are cut by the inductors L1 and L2 and the capacitors C6 and C7 which interconnect corresponding ends of the inductors L1 and L2. General voltage division is attained by the resistors R1 and R2 and the resistor R9 to produce a predetermined output level.
The filter circuit 9 having such a construction as described above filters only a frequency band necessary for reading of data and outputs it to the reading circuit 5.
The reading circuit 5 differentiates signals from the filter circuit 9 and shapes waveforms of the signals into pulse signals including digital codes of 0 and 1. The pulse signals are outputted to the host computer (not shown).
The writing circuit 8 converts input data from the host computer into a level of voltage in accordance with recording and reproducing characteristics of a magnetic disk for 2 megabytes and of the magnetic head 1. The input data thus converted is delivered to the magnetic head 1 via the change-over circuit 2. In this instance, the change-over circuit 2 has been changed over, in response to an instruction from the host computer, to connect the magnetic head 1 to the writing circuit 8.
However, a magnetic recording and reproducing apparatus for 2 megabytes as described above presents problems as hereinafter described when one tries to record in a format different in recording period such as for 1 megabyte, causing an error in operation although a magnetic disk of the same shape is used and is rotated at the same speed. Such problems will be described with reference to FIGS. 3 and 4.
FIG. 4 illustrates operations of different portions of the circuit of FIG. 3 when information recorded in a recording format for 1 megabyte on a magnetic disk for 1 megabyte using a floppy disk drive unit for 2 megabytes is read out on another disk drive unit for 1 megabyte.
Upon writing, input data of a recording period for 1 megabyte corresponding to digital codes including 1 and 0 as seen in (a) of FIG. 4 are delivered from the host computer to the writing circuit 8 of a floppy disk drive unit for 2 megabytes. In response to the input data, the writing circuit 8 supplies to the magnetic head 1 a writing current of a value I1 for 2 megabytes in a recording period for 1 megabyte as seen in (b) of FIG. 4. A magnetic disk for 1 megabyte recorded with the magnetic head 1 has written thereon a magnetic pattern in which the magnetization polarity is reversed in alternate relationship as indicated by N and S in (c) of FIG. 4 with variations in magnetization intensity as shown by a solid line in (d) of FIG. 4.
If the magnetic disk recorded in this way are reproduced on another floppy disk drive unit for 1 megabyte, a voltage of a waveform as shown in (e) of FIG. 4 is outputted from its magnetic head. A portion of the waveform called a shoulder as indicated by S1 to S5 is caused due to an excessively high resolution of writing characteristics of the magnetic head for 2 megabytes relative to the writing characteristics of the magnetic head for 1 megabyte. The difference in resolution arises mainly from magnetic gaps. The voltage waveform (e) from the magnetic head is delivered to the reading circuit via the filter circuit for 1 megabyte and is differentiated thereby into a waveform as shown in (f) of FIG. 4. The waveform (f) thus differentiated is then converted into a square wave signal as shown in (g) of FIG. 4 of a zero volt comparator or the like and then into pulse signals as shown in (h) of FIG. 4 in accordance with variations of the square wave signal. The pulse signals are then coupled to the host computer. The pulse signals (h) involve error pulses E1 to E5 caused by appearances of the shoulders S1 to S5 as described above. If the error pulses E1 to E5 are inputted to the host computer, this will result in inputting of unnecessary additional pulses for a period for 1 megabyte to the host computer. As a result, an output of the host computer will involve error portions as shown by E in (i) of FIG. 4, and the error portions will be outputted as 1 despite that the magnetization polarity as shown in (c) of FIG. 4 is not reversed as in the error pulses E2 and E4, causing an error in operation.
In addition to the problems described above, particularly where a magnetic disk recorded with a floppy disk drive unit for 1 megabyte is additionally recorded with another magnetic head for 2 megabytes, it is actually impossible to effect a filtering operation to discriminate, upon reproduction, additionally recorded signals from the formerly recorded signals. Accordingly, additional recording must be done after additional information has been rewritten in an appropriate recording period, and this requires much time.